There have been a number of reports on a method in which a film is formed using a condensation product of water and a tetraalkoxysilane, and a member to be treated is subjected to inorganic-organic hybrid coating with the film (NPL 1).
However, the above-mentioned condensation product has a small distance between the poles of silicon atoms, and hence poses a problem in that a film obtained by applying the condensation product and heating it is rigid. Especially when this film is formed on a fastening member, it has been difficult to achieve both a corrosion resistance and a function, such as a coefficient of friction, at the same time.
Further, a coating liquid containing the above condensation product has a problem about the stability, for example, a problem in that a hydrolysis proceeds with the passage of time, so that the coating liquid cannot keep the sol-gel properties.